1. Field of the Invention
The present invention relates to a field of a fluid pressure actuator, and more specifically relates to an improved technique about a composite operation type actuator for causing a rod to perform a motion that combines a reciprocating motion with an oscillating motion. In particular, in the composite operation type actuator of the present invention, a direct-acting type actuator section and an oscillating type actuator section are coupled in series to perform a composite operation. Then, with a simple configuration in which a sequence valve with check valve and a throttle valve (or a stop valve) are respectively interposed in passages connecting respective cylinder chambers of the actuator sections, the composite operation is rationally performed just by working fluid distribution switching control over two ports.
2. Description of the Related Art
For setting and extracting core pins for die-casting molds, fluid pressure actuators have been traditionally used.
In this case, extraction of the core pin is performed in a state where molten metal is cooled in a cavity and solidified or semi-solidified. Since the molten metal is cooled and contracted for solidification, scuffing or seizure tends to occur between the core pin and a product.
Accordingly, it has become common practice to apply a draft angle to the core pin so as to facilitate detachment of the core pin, thereby preventing generation of a defective product.
However, a drill formed for the core pin with the draft angle is scarcely used without alteration. Thus, an additional work for modifying the drill to a straight one is applied after molding has been performed. This has therefore become a factor for leading to an increase in the cost of the product.
On the other hand, a lot of fluid pressure actuators for causing a piston rod to perform a motion that combines an oscillating motion with a reciprocating motion have been proposed for a long time. If the actuator of this type is used, it becomes possible to extract the core pin while being rotated or after having been rotated.
More specifically, just by extracting the core pin in the axial direction of the actuator, the product tends to be defective due to scuffing or seizure. However, if extraction of the core pin with rotation is performed, the core pin can be extracted comparatively easily without laboring. Especially in a state where the molten metal is semi-solidified under a certain condition, it sometimes becomes possible to form a drill with an extremely high precision even if the draft angle is not applied to the core pin.
Then, among the actuators that have implemented the motion that combines the oscillating motion with the reciprocating motion are the actuators disclosed in a. Japanese Patent Examined Publication SH046-33457, b. Japanese Utility Model Examined Publication SH063-29921, c. Japanese Utility Model Unexamined Publication HEI01-118203, d. Japanese Utility Model Unexamined Publication HEI02-14803, and e. Japanese Patent Publication No.2875220, for example.
In the publications a. to c., the composite operation type actuator using either of the following methods is proposed: A pinion is directly mounted to the piston rod of a direct-acting type actuator for the reciprocating motion so that it forms the constrained pair of only a sliding pair with the piston rod of the direct-acting type actuator, or the pinion is fixed to a shaft rod fitted inside a hollow opening formed from the rear surface of the piston rod in the axial direction so that the axial rod forms only the sliding pair with the hollow opening. Then, a rack to be meshed with the pinion is moved by another direct-acting type actuator for the oscillating motion.
On the other hand, the publication d. discloses the composite operation type actuator shown in FIG. 18(A).
This actuator is constituted from a direct-acting type actuator section 100 and an oscillating type actuator section 120 of a cylinder structure. The oscillating type actuator section 120 is coupled in series to a head cover 102 of the direct-acting type actuator 100 so that an oscillating shaft 121 of the oscillating type actuator section 120 is arranged on the same axis as a piston rod 101 of the direct-acting type actuator section 100.
The direct-acting type actuator section 100 constitutes a structure of a single rod double-acting cylinder, and in a piston rod 101 thereof, a hollow opening 103 is formed from a rear surface of the piston rod in the axial direction.
The oscillating type actuator section 120 also has a cylinder structure, in which the oscillating shaft 121 is rotatably supported by radial bearings 124 and 125 provided for covers 122 and 123 at the front and the back of the oscillating type actuator section 120, respectively.
On the oscillating shaft 121, a ball screw 127 is formed in a section within a cylinder tube 126, and an opening for causing the oscillating shaft 121 to pass through a piston 128 is formed in the piston 128. This opening constitutes a screw opening 129, and balls (not shown) are interposed between the ball screw 127 on the side of the oscillating shaft 121 and the screw opening 129 on the side of the piston 128.
Further, a protrusion 130 is formed on the outer periphery side of the piston 128, and this protrusion 130 is loosely fitted into a guide opening 131 in the axial direction formed in the cylinder tube 126.
The front section of the oscillating shaft 121 is inserted inside the hollow opening 103 of the piston rod 101, after penetrating the head cover 102 of the direct-acting type actuator section 100.
Then, in the section where the oscillating shaft 121 is inserted inside the hollow opening 103, sections 121a at opposed locations of the outer peripheral surface of the oscillating shaft 121 are formed in a planar form. Then, as shown in FIG. 18(B), a bush 104 secured to the rear end of the hollow opening 103 of the piston rod 101 causes the front section of the oscillating shaft 121 to be inserted inside the hollow opening 103 to form the constrained pair of only a sliding pair with the hollow opening 103 of the piston rod 101.
Incidentally, a section in the hollow opening 103 of the piston rod 101, in front of the leading edge of the oscillating shaft 121, should be linked to the cylinder chamber on the side of the head cover of the direct-acting type actuator section 100. The publication d., however, does not give a description about this configuration.
As shown in FIG. 18(A), the direct-acting type actuator section 100 and the oscillating type actuator section 120 of this composite operation type actuator are separately controlled by four-port three-position switching valves 141 and 142, respectively.
More specifically, according to this composite operation type actuator, distribution control of a working fluid over distribution ports 105 and 106 using the four-port three position switching valve 141 enables the piston rod 101 to reciprocate. Further, distribution control of the working fluid over distribution ports 132 and 133 using the four-port three-position switching valve 142 enables the piston 128 to be moved to and fro, thereby enabling rotation of the oscillating shaft 121. Since these controls can be independently executed at arbitrary timings, the motion of the piston rod 101 that combines the reciprocating motion with the oscillating motion can be freely performed.
One of the inventors of the present invention is the co-inventor of the above-mentioned publication e. The publication e. discloses a cylinder device suitable for setting and extracting the core pin. The cylinder device implements the operation of rotating the piston rod during a final certain period of the thrusting step of the core pin and an initial certain period of the drawing-in step of the core pin alone. For the period other than these periods, the rod is not rotated.
According to the composite operation type actuator in the above-mentioned publication d., the above-mentioned motion of the piston rod 10 that combines the reciprocating motion and the oscillating motion can be executed at an arbitrary timing.
However, in order to individually control the direct-acting type actuator section 100 and the oscillating type actuating section 120, the two four-port three-position switching valves 141 and 142 are necessary, and the cost of an overall system including a peripheral fluid circuit and a sequence control system becomes rather high.
Further, the composite operation type actuator described above requires four tubing. When a lot of the actuators for actuating the core pin are integrated into the die-casting mold, the number of tubing for the mold becomes extremely great, so that tube arrangement becomes complicated. At the same time, when a space for installing the actuators cannot be sufficiently secured, design of the die-casting mold becomes difficult.
On the other hand, in the case of the actuator for operating the core pin, it is enough that the operation of retracting the piston rod while being rotated from a forward limit position or the operation of retracting the piston rod after having being rotated can be performed, and the operation that combines the reciprocating motion with oscillating motion in a complicated sequence is not required.